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zoti Samba Member
Joined: December 26, 2007 Posts: 2061 Location: Plano, TX USA
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Posted: Wed Aug 04, 2021 3:41 pm Post subject: Using my solar to keep starting battery topped off |
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I have a solar setup with 2 100W AGM batteries and a 100W panel on top.
My van sits and after a few weeks of not running the starter battery will get too weak. I charge it back up with a battery charger and it will work fine as long as I drive the car but will again goo too low after sitting.
I'd like to use the solar to also trickle charge the main battery.
I already have a setup that enables me to charge the AGM batteries while the engine is running off the alternator so I am wondering what I need to do the opposite and charge the starter battery off the solar. |
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fxr Samba Member
Joined: December 07, 2014 Posts: 2325 Location: Bay area CA
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Posted: Wed Aug 04, 2021 4:10 pm Post subject: Re: Using my solar to keep starting battery topped off. |
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What voltage do your AGM batteries get to when charged? If they routinely go to more than ~13.8V, then a simple diode (with a switch) will do the deed for you. Doesn't have to be a big one, a 6A one will suffice. However, it must be switched so that the AGM batteries don't try to help the starter when starting, as that will blow the diode. Assuming you have some sort of relay that does this already to disconnect the alternator from the AGM batteries when starting, then you just need another relay with its coil in parallel with the first one to switch the diode.
https://www.amazon.com/gp/product/B007Z7OQ5G
Less than $15 all told.
The much more expensive way is to invest in a Renogy or Victron DC-DC charger which will automatically take care of the starter battery as well as the AGM ones. $200 upwards. However, this also makes you Lithium battery capable should you wish to do that in the future. _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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jimf909 Samba Member
Joined: April 03, 2014 Posts: 7473 Location: WA/ID
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Posted: Wed Aug 04, 2021 10:53 pm Post subject: Re: Using my solar to keep starting battery topped off |
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OP, it sounds like you have a solar controller to charge the aux. AGM batteries. It also sounds like you have some sort of arrangement to send alternator current to both the starter battery and AGM aux. batteries.
It sounds like you want to send current from the solar panels to the starter battery when the van is idle for weeks. A few ideas from rudimentary to fancier:
- A simple jumper from the post of an aux battery to the starter (assuming they share a ground).
- FXR's suggestion
- a battery combiner such as a Yandina that will automatically combine batteries when voltage exceeds 13v on one side (alternator to aux. batteries when driving, solar to starting battery when on solar). This won't be an optimal charge pattern but it's waaay better than allowing a starting battery to repeatedly drop to 50% SOC.
- and so on...
The single most important thing is to not allow the starter battery to repeatedly drop to 12.4, 12.3. 12.2 volts or lower. That'll eliminate recharge cycles from the battery's life.
Is your van w/in reach of an AC outlet? If so, consider keeping the starter and aux systems separate and just set up a battery maintainer plugged into AC to keep the starter battery charged. _________________ - Jim
Abscate wrote: |
Do not get killed, do not kill others.
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Current: 1990 Westy Camper - Bostig RG4, 2wd, manual trans w/Peloquin, NAHT high-top, 280 ah LFP battery, 160 watts solar, Flash Silver, seam rust, bondo, etc., etc.
Past: 1985 Westy Camper - 1.9 wbx, 2wd, manual trans, Merian Brown, (sold after 17 years to Northwesty who converted it to a Syncro). |
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dobryan Samba Member
Joined: March 24, 2006 Posts: 16505 Location: Brookeville, MD
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Gnarlodious Samba Member
Joined: September 28, 2013 Posts: 2323 Location: Adobe Jungle USA
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Posted: Thu Aug 05, 2021 6:35 am Post subject: Re: Using my solar to keep starting battery topped off |
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For this I installed a cheap programmable voltage controller that switches on the relay at about 13.6 volts. Search eBay for a device called a “12v voltage control switch overvoltage protection module”. I actually wrote a whole post about this solution:
How to safely run a flooded and AGM battery together _________________ Vanagon ’83 diesel AAZ w/Giles injection, 5spd 4.57R&P+TBD and a '78 diesel Rabbit |
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4Gears4Tires Samba Member
Joined: October 08, 2018 Posts: 3051 Location: MD
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Posted: Thu Aug 05, 2021 7:17 am Post subject: Re: Using my solar to keep starting battery topped off |
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dobryan wrote: |
If you are outside and the front faces something like South get a small 10W solar panel that sits on the dash and plugs into the stock cig lighter socket on the dash. I do this for the euroBus and it works great to keep the starting battery topped up while sitting. |
You don't need a controller? _________________ '87 Syncro
Ferric Oxyhydroxide Superleggera Edition |
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dobryan Samba Member
Joined: March 24, 2006 Posts: 16505 Location: Brookeville, MD
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fxr Samba Member
Joined: December 07, 2014 Posts: 2325 Location: Bay area CA
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Posted: Thu Aug 05, 2021 9:02 am Post subject: Re: Using my solar to keep starting battery topped off |
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4Gears4Tires wrote: |
dobryan wrote: |
If you are outside and the front faces something like South get a small 10W solar panel that sits on the dash and plugs into the stock cig lighter socket on the dash. I do this for the euroBus and it works great to keep the starting battery topped up while sitting. |
You don't need a controller? |
Not for 15W solar or less. The current they can provide is less than the tiny trickle that is allowed for LA batteries long term. (C/500 IIRC) _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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Andymon Samba Member
Joined: February 24, 2015 Posts: 314 Location: Medford, OR
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4Gears4Tires Samba Member
Joined: October 08, 2018 Posts: 3051 Location: MD
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Posted: Thu Aug 05, 2021 9:55 am Post subject: Re: Using my solar to keep starting battery topped off |
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Oh cool. Very handy for my rallycross car that has a slow electrical leak. I think it's the keyless entry which I don't want to remove. This is easy enough to throw on the back seat shelf.
Thanks! _________________ '87 Syncro
Ferric Oxyhydroxide Superleggera Edition |
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Abscate Samba Member
Joined: October 05, 2014 Posts: 22670 Location: NYC/Upstate/ROW
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Posted: Thu Aug 05, 2021 1:10 pm Post subject: Re: Using my solar to keep starting battery topped off |
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In 4 weeks a good battery will lose 15-20% charge max.
If it won’t start your car, it’s dead, Jim.
Check for parasitic drains _________________ .ssS! |
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